Question

Read the following statements (A-D). How many of the following statements are correct regarding the immune response during vaccination?

A. Antigens are sensed as foreign substances by different antigen-presenting cells (APCs) like RBCs.
B. Antigen-presenting cells initiate immune response by engulfing the antigens and processing them.
C. A naive T cell identifies the antigen presented by macrophages and gets activated.
D. Upon activation by cytokines, the naive B cells divide to form memory B cells.

• A. 3
• B. 2
• C. 1
• D. 4

Answer 1

The correct option is A 3

The response of the immune system to any foreign substances (pathogens/toxins) is called immune response. It is of two types, primary immune response and secondary immune response.

The immune response produced by the body during its first encounter with an antigen (any foreign substance capable of generating an immune response) is called primary immune response.

If the body subsequently encounters the same antigen, the immune response produced differs from the primary immune response, as there is an increased production of antibodies and immune cells. This is called secondary immune response which is usually very fast.

Vaccination refers to the administration of any vaccine. Vaccines elicit primary immune response to a specific antigen derived from an infectious disease-causing pathogen.

This results in the production of the memory B cells and T cells which provide immunity upon exposure to the similar antigens.

The initial immune response (primary immune response) upon the administration of the vaccine is as follows:

1. Antigens entering the body are sensed as foreign substances by different antigen-presenting cells (APCs) like macrophages. RBCs cannot act as antigen-presenting cells. Hence statement A is incorrect.

2. Antigen-presenting cells initiate primary immune response by engulfing the antigens and processing them. So, statement B is correct.

Processing involves the partial degradation of the antigen by the macrophage and thereby only the immunogenic (can elicit immune response) portion of the antigen is retained.

3. The macrophage, along with the processed antigen on its surface, presents the antigen to the naive T cells.

4. The naive T cells identify the presented antigen on the macrophages and get activated. So, statement C is correct.

5. Now naive T cells get converted into T helper cells and start releasing chemicals called cytokines. The cytokines diffuse and reach naive B cells. The receptors of naive B cells pick up these cytokines and the B cells are triggered to divide and form memory B cells. These memory B cells will remain in the body for a long time and provide immunity on coming in contact with antigens by producing antibodies (secondary immune response). Hence statement D is correct.

Figure: Primary immune response